Galaxy Slam Captured by Hubble

April 24, 2008 -- What might be described as the universe's mightiest sumo matches, or perhaps rowdiest square dances, have been caught on camera and brought together for the first time into an extraordinary album of galactic collisions.

Each image, captured by the Hubble Space Telescope (HST), is a snapshot of an ongoing process of galaxies slamming or twirling into each other.

"The gravitational dance is taking place over hundreds of million of years," explains Hubble researcher Lars Lindberg Christensen of the European Space Agency (ESA) in Garching, Germany. "A lot of the same things are happening, but still a lot of different things happen as well."

For instance, some images show galaxies just beginning to collide while others show the process well underway. There are also differences in the speeds of the collisions, it appears. Some galaxies look sort of like a water balloon being punctured by a bullet, Christensen told Discovery News.

Despite the violent appearances, however, the stars within the galaxies are not themselves colliding, since they are too far apart. All the action is really in the gases and dust, which do collide and create terrific shockwaves.

These shocks are thought to then trigger vast waves of star creation. In fact it's the heat of all those new stars -- in the form of infrared light collected by the HST -- that gave away the collisions in many of these images.

"Collisions basically result in rampant star formation in galaxies as gas is compressed by the interaction," said astronomer Aaron Evans of the University of Virgina, Stony Brook University and the National Radio Astronomy Observatories. "It turns out that most of the star formation in these galaxies is obscured, and thus the light from these stars is absorbed by dust and emitted as heat."

This heat is also the best handle astronomers have on the overall importance of merger-induced star formation comes from measuring the total energy budget of the Universe, said Evans. Astronomers figure that about half of the light generated since the Big Bang is infrared light -- mostly generated in these sorts of galactic mergers.